Conventional fuel injection systems utilize a fuel pump to provide fuel to a fuel injection supply manifold having a fuel rail which carries fuel to a plurality of fuel injectors. A pressure regulator is mounted in the fuel flow path so as to maintain the fuel pressure in the rail at approximately 40 psi greater than engine intake manifold vacuum. The pump, typically mounted in the fuel tank, runs at a constant speed and may deliver, for example, 90 liters per hour. When idling, the engine needs only about 3 liters per hour and, therefore, 87 liters per hour must be returned to the fuel tank through a return line. This returned fuel usually has an increased temperature as a result of being routed to the engine and thus frequently evaporates upon reaching the relatively lower pressure and temperature of the fuel tank. The fuel vapor so generated either remains in the tank until vented to atmosphere, which potentially creates environmental problems, or until captured in a vapor storage container, such as a carbon canister, which requires additional manufacturing expense.
In any case, the problems associated with fuel vapor generation in conventional fuel systems have led fuel system designers to develop a returnless fuel supply system, such as that disclosed in U.S. Pat. No. 5,237,975 (Betki et al.), assigned to the assignee of the present invention. In such a system, fuel rail pressure is controlled for precise fuel mass flow to the injectors at both normal and elevated engine temperatures by varying fuel pump speed as a function of assorted variables, including fuel temperature. As a result, the fuel temperature must be accurately measured without interfering with fuel flow in the rail.
The present invention provides a means to measure fuel temperature without obstructing fuel flow while also providing an end closure for the rail with a fuel inlet, all in a unitary component. An end closure device is required since molding, extruding, or forging of fuel rails typically leaves an opening or aperture at the longitudinal ends of the fuel rail. These openings are usually closed with a cap or plug, as shown in U.S. Pat. No. 5,197,435 (Mazur et al.), U.S. Pat. No. 4,570,600 (Atkins, et al.) and U.S. Pat. No. 4,601,275 (Weinand), to prevent fuel leakage from the rail. Such caps may have a barbed type hose connection in the end cap, such as disclosed in U.S. Pat. No. 4,474,159 (Katnik), with a pressure regulator inserted on the other end of the rail. Other end closure devices may have a fuel inlet nipple brazed therein and a threaded fitting for a fuel line to a pressure monitor or a pressure regulator in the top of the rail adjacent the fuel inlet nipple, as seen in U.S. Pat. No. 4,519,368 (Hudson, Jr.). However, the aforementioned do not provide a unitary component for end closure and fuel inlet while also integrating a fuel parameter measurement mechanism therein, such as a fuel temperature sensor.